Micro-display projection systems using a reflective light engine or imager, such as digital light pulse (DLP) imager, are increasingly utilized in color image or video projection devices (e.g., rear projection television (RPTV)). In an existing projection system, shown in FIG. 1, a light source 10 is provided, in this case a UHP lamp generates white light (i.e., all color spectrums). Light from the light source 10 passes through a color wheel 20 which has a plurality of dichroic filtering elements, each of which allows a light band of one of the colors: blue, green and red to pass through and reflects light of the other colors. The color wheel 20 is rotated so that a temporal pattern of blue, green, and red light bands pass through the color wheel. The color wheel is typically rotated fast enough to create at least one primary color period for each primary color during each frame of a video image. Rotating the wheel faster, or using multiple filter segments for one or more of the primary colors can produce color separation artifacts that allow the viewer to detect the sequential color nature of the display system. For example, color breakup, also called the rainbow effect, is caused by light passing through a rotating color wheel with colors flashing sequentially and appears as a momentary flash of rainbow-like striping typically trailing bright objects when looking quickly from one side of a viewing screen to the other, or when quickly looking away from the viewing screen to an off-screen object. Additionally, color edge effects appearing as a flash of one of the three primary colors in the sequential color light beam at a leading edge of a moving object across the screen may also produce color separation artifacts.
An integrator 30 receives the light band from the light source 10 that is allowed to pass through the color wheel 20 and directs the light band through relay optics 40 into a total internal reflection (TIR) prism 50. The TIR prism 50 deflects the light band onto an imager 60, such as a DLP imager. The imager modulates the intensity of individual pixels of the light beam and reflects them back through the TIR prism 50 and into a projection lens system 70. The projection lens system 70 focuses the light pixels onto a screen (not shown) to form a viewable image. A color video image is formed by rapid successive matrices of pixels of each of the three colors (blue, green, and red) which are blended by the viewer's eye to form a full color image.
Throughout this specification, and consistent with the practice of the relevant art, the term pixel is used to designate a small area or dot of an image, the corresponding portion of a light transmission, and the portion of an imager producing that light transmission.
The DLP imager 60 comprises a matrix of micro-mirrors, moveable between an angle that reflects light through the TIR prism 50 and into the projection lens system 70 and an angle that deflects the light so that it is not projected by the projection lens system 70. Each micro-mirror reflects a pixel of light of a desired intensity depending upon a succession of angles of that particular micro-mirror which in turn are responsive to a video signal addressed to the DLP imager 60. Thus, in the DLP imager 60, each micro-mirror or pixel of the imager modulates the light incident on it according to a gray-scale factor input to the imager or light engine to form a matrix of discrete modulated light signals or pixels.
Existing DLP imagers, however, suffer from several problems. The color wheel wastes light, as the light having the colors that are reflected is typically lost. Also, color separation or break-up artifacts degrade the image quality of the projection system, as described above. Additionally, each micro-mirror may pivot up to twelve times for each of the three color bands for each frame, limiting the frame speed and adversely effecting mechanical reliability. As such, a system for reducing color separation or breakup artifacts and/or having improved resolution and improved reliability is needed.